This project is intended to study the cytokinetic effects of various chemotherapeutic agents on both tumor (leukemic AKR thymocytes) and normal host tissue (bone marrow of non-leukemic mice or normal elements of leukemic bone marrow). The objective of this study is to characterize the differential kinetic effects of chemotherapy on tumor and on normal host tissues as a function of chemotherapeutic agents, dose and time. It is hoped that such data will contribute toward the development of rational programs of chemotherapeutic scheduling. The tumor cells will be studied as to absolute cell number, as to numbers of tumor colony forming units, and as to proliferative characteristics reflected by labeling index, DNA content distribution, and growth rate. Normal bone marrow will be studied as to numbers of splenic colony forming units (CFU-S), colony forming units in culture (CFU-C), and erythroid colony forming units (CFU-E). Additionally labeling index of nucleated marrow cells will be determined and cycling characteristics of colony forming units will be assessed by hydroxyurea suicide. Chemotherapeutic agents studied will be two doses each of methotrexate, and cytosine arabinoside. Recovery rate of the above parameters will be correlated with chemotherapeutic effect, with such data being compared to data on optimal scheduling of chemotherapeutic agents.